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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sOzA0-00000001otM-0HqV; Wed, 03 Jul 2024 12:32:32 +0000 Date: Wed, 3 Jul 2024 13:32:31 +0100 From: Matthew Wilcox To: Vlastimil Babka Cc: linux-mm@kvack.org, David Rientjes , Christoph Lameter , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Roman Gushchin , Kees Cook , Alice Ryhl , Boqun Feng , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, patches@lists.linux.dev Subject: Re: [PATCH v2] slab, rust: extend kmalloc() alignment guarantees to remove Rust padding Message-ID: References: <20240703072520.45837-2-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240703072520.45837-2-vbabka@suse.cz> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 2F81D8000E X-Stat-Signature: nt77ys3yw1dtyhfp48jx9t585xk7k7fr X-HE-Tag: 1720009958-134603 X-HE-Meta: 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 aAQeZ8QK si5Z1VtlQrjdDf+pQKciSBaHoNXm8D5f3q8pvQjSJJnlE6re/wV9LFMy+HPwqWEzBIjlc5v2kiXUmuTsTE2WrUk0RaPU9E7pRInp6oAlKYVULu4ajJ7Bzet7ZGvKSMGBVABqFzIYCrQ2lhziFysN+j20h5PbJxE2oQWISBcBXtafF//s2ayPPlDm/krNwRDEtkUTsOJbqA6JKMboT4D9Ya76zWHQ26qTdVqFjs+mOFVonVahCdzxuVimHNi1mT4u8O1FC6IDZUlcb/iaGOW1NLyabzA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 03, 2024 at 09:25:21AM +0200, Vlastimil Babka wrote: > - if (is_power_of_2(size)) > - align = max(align, size); > + if (flags & SLAB_KMALLOC) > + align = max(align, 1U << (ffs(size) - 1)); hmm ... maybe this would be faster: if (flags & SLAB_KMALLOC) { u32 tmp = size & (size - 1); align = max(align, size - tmp); } (if size is 2^n, tmp is 0. otherwise, tmp is size with the lowest bit clear, so size-tmp is the largest POT that divides size evenly)